A 3-hydroxy-.gamma.-butyrolactone derivative is used as an intermediate in making medicines and agrochemicals. The known methods for preparing it are as follows: (i) The method by reacting 3-hydroxy-.gamma.-butyrolactone with lithium diisopropylamide to form a dianion, followed by adding an alkylating agent (J. Org. Chem., 46, 4319 (1981)). (ii) The method of preparing a 3-hydroxy-.gamma.-butyrolactone derivative by using 2-butenoic acid as a starting material (J. Chem. Res. (S), 274 (1996)).